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Serratrice, L and De Cat, C orcid.org/0000-0003-0044-0527 (2020) Individual differences in the production of referential expressions: The effect of language proficiency, language exposure and executive function in bilingual and monolingual children. Bilingualism: Language and Cognition, 23 (2). pp. 371-386. ISSN 1366-7289
https://doi.org/10.1017/S1366728918000962
© 2019, Cambridge University Press. This article has been published in a revised form in Bilingualism: Language and Cognition https://doi.org/10.1017/S1366728918000962. This version is free to view and download for private research and study only. Not for re-distribution, re-sale or use in derivative works.
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Referential choice in bilingual and monolingual children
Individual Differences in the Production of Referential Expressions: The Effect of Language Proficiency, Language Exposure and Executive Function in Bilingual and Monolingual Children* Ludovica Serratrice, University of Reading Cécile De Cat, University of Leeds *Acknowledgments This research was funded by a grant from the Leverhulme Trust (RPG-2012-633), which is gratefully acknowledged. Special thanks to Sanne Berends for leading on data collection and coding, and to Furzana Shah for assistance with the data collection. Many thanks to Arief Gusnanto for statistical consultancy, and to the many schools who opened their doors to our project, to the participating children for their enthusiasm and their efforts, and to their parents for filling in lengthy questionnaires. Address for correspondence: Ludovica Serratrice University of Reading School of Psychology and Clinical Language Sciences Harry Pitt Building Reading RG6 7BE [email protected]
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One hundred and seventy-two English-speaking 5- to 7-year-olds participated in a
referential communication task where we manipulated the linguistic mention and the
visual presence of a competitor alongside a target referent. Eighty-seven of the
children were additionally exposed to a language other than English (bilinguals). We
measured children’s language proficiency, verbal working memory (WM), cognitive
control skills, family SES, and relative amount of cumulative exposure and use of the
home language for the bilinguals. Children’s use of full Noun Phrases (NPs) to
identify a target referent was predicted by the visual presence of a competitor more
than by its linguistic mention. Verbal WM and proficiency predicted NP use, while
cognitive control skills predicted both the ability to use expressions signalling
discourse integration and sensitivity to the presence of a discourse competitor, but not
of a visual competitor. Bilingual children were as informative as monolingual
children once proficiency was controlled for.
Keywords: referential choice, anaphora, individual differences, cognitive control,
gradient bilingualism
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One of the core aspects of human communication revolves around the choice
of linguistic expressions for referent identification, i.e. the use of proper names (e.g.
Laura), Noun Phrases – NPs - (e.g. the girl, my sister, my sister’s car) and pronouns
(e.g. she, them, someone) to talk about entities in the world. Adults, and, to some
extent, preschool and school-age children are sensitive to a number of structural,
semantic and discourse-pragmatic constraints when it comes to producing referential
expressions in a communicative context (see Serratrice & Allen, 2015, for an
overview of the acquisition of reference).
Despite a general sensitivity to the aforementioned constraints, there are
individual differences in the extent to which both adults and children rely on
perspective-taking skills to process and produce referential expressions. Taking the
perspective of a conversational partner requires the inhibition of one’s own
perspective and the shifting to that of the addressee. Recent work on adult speakers
(Ryskin, Benjamin, Tullis & Brown-Schmidt, 2015; Wardlow, 2013), and some
emerging work in child and adolescent speakers (Nilsen & Graham, 2009; Nilsen,
Varghese, Xu & Fecica, 2015; Torregrossa, 2017; Wardlow & Heyman, 2016), has
identified executive function skills, particularly working memory (WM), and
cognitive control, i.e. the ability to resolve a conflict by inhibiting an irrelevant
response and promoting relevant information, as significant predictors of individual
variation in referential communication success. The use of a referential expression
implies a choice, for example a pronoun vs. a NP. This choice arises from the
selection between different options and, at least in some cases, it is the outcome of the
resolution of a conflict between competing alternatives. For example, if the speaker
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and the addressee have different levels of access to a target referent, their mental
representations will not entirely overlap. The onus is on the speaker to inhibit a
potentially egocentric perspective and promote an addressee-friendly perspective that
will maximise the chances of convergence between the mental representations of both
speaker and addressee. This can translate into choosing a more informative NP (e.g.
the tall girl), as opposed to a more reduced and less informative expression (e.g. she).
Because conflict monitoring and resolution depend on the inhibition of irrelevant
information, the promotion of relevant information, or both, we will adopt the term
cognitive control to include both the inhibition and the promotion aspects of the
process (Teubner-Rhodes, Mishler, Corbett, Andreu, Sanz-Torrent, Trueswell &
Novick, 2016).
WM refers to the ability to store and manipulate information, and it has been
connected to perspective-taking and referential choice in at least two ways. Firstly, it
underpins the storage and updating of the interlocutor’s perspective and the
comparison of that perspective with one’s own to check for convergence (Nilsen &
Bacso, 2017; Wardlow, 2013). Secondly, it may be implicated in the use of feedback
in the case in which one of the interlocutors explicitly signals a mismatch between
their perspective and that of their conversational partner. Higher verbal WM capacity
has been shown to correlate positively with 5- and 6-year-olds ability to use an adult’s
non- verbal feedback to produce a discourse-appropriate referential expression
(Wardlow & Heyman, 2016).
A parallel line of research has singled out bilingual speakers – both older
adults and children - as having an advantage in the same executive function skills of
cognitive control that are associated with referential choice (Bialystok & Martin,
2004; Morales, Calvo & Bialystok, 2013). Whether bilinguals genuinely have
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superior WM skills compared to monolinguals, or not, is, however, not yet clear.
Some studies report no difference between bilingual and monolingual children
(Barbosa, Jiang & Nicoladis, 2017; Bialystok, Luk, and Kwan 2005; Engel de Abreu,
2011), others report an advantage for bilingual children (Morales, Calvo, & Bialystok,
2013).
In the present study we combine these two independent lines of inquiry to
investigate how degrees of exposure to/and use of English and another home
language, language proficiency in English, and executive function skills (cognitive
control and verbal WM), predict the choice of linguistic expressions in a referential
communication task in monolingual and bilingual children between the ages of 5 and
7. In the task we manipulated a linguistic factor (the discourse mention of a
competitor to the target referent) and a non-linguistic factor (the visual presence of a
competitor to the target referent) to provide new evidence on the sources of contextual
information used by children in reference production. Previous work has focused on
children’s use of deictic expressions in referential communication tasks (e.g. Nilsen &
Graham, 2009), while we were specifically interested in children’s use of anaphoric
expressions to refer to a previously mentioned antecedent.
Research including bilingual children has sometimes neglected to take into
account the SES profile of participants. This is an important limitation as SES is
known to be predictive of both language and of cognitive skills. In the present study
we therefore included a measure of SES in our analyses.
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Adult speakers are sensitive to a number of structural and discourse-pragmatic
constraints in their referential choices. They tend to use more pronouns for referents
that are in subject position (Arnold, 2001) and/or in sentence-initial position
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(Järvikivi, van Gompel, Hyönä & Bertram, 2005), or for referents that are topics
(Anderson, Garrod & Sanford, 1983). Conversely, competent speakers tend to use
more informative referential expressions (e.g. proper names and indefinite NPs) when
the referent is new to the discourse (Gordon, Hendrick, Ledoux & Yang, 1999), or
when the use of a pronoun might lead to potential ambiguity (Arnold, 2008). Adult
speakers generally can take the perspective of their listener into account, and they
choose their referential expressions accordingly. Perspective-taking is predicated
upon the ability to distinguish between what is in the common ground (Clark, 1992),
and therefore shared knowledge between speaker and listener, and what is in the
privileged ground, i.e. knowledge that is only accessible to the speaker. The common
ground can either be established perceptually, i.e. when it includes referents that are
visually accessible to both interlocutors, and/or it can be established linguistically via
the use of discourse-appropriate referential expressions.
Competent adult speakers typically engage in modelling their addressee’s
perspective to produce a referential expression that is optimal for their conversational
partner (Hendriks, Englert, Wubs & Hoeks, 2008). In essence the assumption is that
competent speakers maintain their onw mental representation of their addressee’s
mental representation. However, the extent to which these meta-representations
always require an effortful and intentional commitment on the part of the speaker, and
whether they necessarily rely on explicit Theory of Mind skills, is debated in the
literature (Horton & Brennan, 2016).
Even before they have a fully developed Theory of Mind, three-year-olds are
already at least partly sensitive to the same constraints that regulate referential choice
in adult speakers (see Allen, Hughes & Skarabela, 2015, for a review). Pre-school
children are more likely to omit arguments, or use reduced expressions, when they are
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part of the common ground either through joint attention (Skarabela, 2007), previous
linguistic mention (Allen & Schröder, 2003; Clancy, 2003; Guerriero, Oshima-
Takane & Kuriyama, 2006; Stephens, 2015), or prior mention and/or perceptual
availability (Campbell, Brooks & Tomasello, 2000; De Cat, 2011; Matthews, Lieven,
Theakston & Tomasello, 2006; Rozendaal & Baker, 2010; Salazar Orvig et al., 2010a;
Salazar Orvig et al., 2010b).
At the same time, children are notoriously less capable than adults when it
comes to taking their listener’s perspective into account and to adjusting their
referential choices accordingly. This has been observed in production studies in pre-
schoolers (De Cat, 2011, 2015), in five-year-olds (Theakston, 2012), and in six-years-
old (Serratrice, 2008) when children need to provide a referential expression, and up
to adolescence in comprehension where participants need to make a choice between
potential referents (Dumontheil, Apperly, & Blakemore, 2010).
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It is becoming increasingly apparent that there are individual differences in the
degree of perspective-taking abilities, and that this variation may correlate with the
ability to interpret referential expressions in discourse-pragmatic appropriate ways
(Brown-Schmidt, 2009; Lin, Keysar & Epley, 2010; Ryskin et al., 2015). Studies on
adults have focused on the relationship between perspective-taking abilities - indexed
by referential choice - and cognitive control and WM - two core components of
executive function. There is some additional evidence that cognitive control also
plays a role in perspective-taking and referential interpretation in pre-school children.
In two referential communication studies with three- and five-year-olds, Nilsen and
Graham (2009) reported that performance on a cognitive control task significantly
predicted comprehension accuracy for both the younger and the older children.
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However neither WM nor cognitive control were predictive of accuracy in a
production task in which the five-year-olds had to provide a disambiguating adjective
to identify a referent in the privileged ground condition. Nilsen and Graham (2009)
speculated that this non-significant finding could be due to the fact that their measure
for assessing children’s perspective taking (i.e. the number of adjectives in the
common ground condition) was not sufficiently sensitive to reveal the impact of
cognitive control.
Some of the adult studies point to a positive correlation between cognitive
control skills and perspective-taking abilities in the online interpretation (Brown-
Schmidt, 2009; Lin et al., 2010) and production of referential expressions (Wardlow,
2013), but others have failed to replicate this finding with monolingual and bilingual
adults in a spatial perspective-taking task (Ryskin, Brown-Schmidt Canseco-
Gonzalez, Yiu, & Nguyen, 2014), and with children with ADHD in a referential
communication task (Nilsen, Mangal & Macdonald, 2013).
Verbal WM (WM) has also been recently linked to individual differences in
perspective-taking skills in the production of referential expressions in monolingual
adults (Wardlow, 2013). Referential choice requires the speaker to focus on those
conceptual features that make the target different from potential competitors that may
or may not be accessible to the addressee. This evaluation process relies on the
storage in memory of the features of the target and it additionally requires a
comparison with the features of the competitors. This is a complex set of operations
that involve both the storage and the manipulation of information. In essence these
demands are comparable to those of a WM task where the information must be
retained in memory while being subjected to additional operations. Adopting a
computational modelling approach, Hendriks (2016) has argued for individual
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differences in WM capacity and processing speed as predictors of informativity in
referential choice. Hendriks (2016) reports on a series of computational simulations
where the manipulation of WM capacity in the network led to significant differences
in the use of pronouns vs. NPs to refer back to a potentially ambiguous antecedent
(van Rij, 2012). In the low WM model there was a significantly higher proportion of
underspecified and underinformative pronouns than in the high WM model where
more pragmatically adequate NPs were used.
The role of verbal WM has not yet been explored in connection with
referential choice in bilingual children. In monolingual children, Nilsen and Graham
(2009) did not find WM to be predictive, possibly because of the relatively low task
demands, but Wardlow and Heyman (2016) found it to be positively correlated with
5- and 6-year-olds’ ability to benefit from adult non-verbal feedback in a referential
production task. Children with higher WM improved their use of discourse-
appropriate referential expressions in the course of the experiment when they received
feedback that they were being uninformative. In a sample of monolingual German-
speaking 8- to 10-year-olds Torregrossa (2017) also found a positive correlation
between WM - indexed by backward-digit-span scores - and the discourse-
appropriate use of demonstrative pronouns in a story-telling task pronouns. In the
light of Wardlow’s (2013) preliminary findings with adult speakers, Torregrossa’s
(2017) findings with 8- to 10-year-olds, and the results in the feedback condition for
the 5- and 6-year-olds in Wardlow and Heyman’s (2016) study, it is theoretically
interesting to test whether the relationship between choice of referring expressions
and verbal WM generalizes to bilingual child speakers
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A parallel but independent line of research has shown, albeit not
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uncontroversially (see Valian, 2015), that cognitive control is one area in which
bilinguals may have an advantage over monolinguals (Bialystok, 2015). If bilingual
children do have an advantage when it comes to inhibiting information that is in their
privileged ground and promoting information in the common ground, and if this kind
of cognitive control is conducive to referential communication, it follows that
bilingual children should, in principle, be more successful in choosing discourse-
appropriate linguistic expressions in a referential communication task that requires
cognitive control. To date no studies have directly investigated whether individual
differences in cognitive control and WM confer an advantage to young bilinguals
when it comes specifically to referential choice. The literature on referential
expressions in bilingual children and adults has principally focused on the issue of
cross-linguistic influence, and on whether the interpretation of third person pronouns
is affected in a null-subject language when the other language has obligatory overt
subjects (Serratrice & Hervé, 2015). More recently some studies with infants and
young children have reported a bilingual advantage for sensitivity to referential cues
(Fan, Liberman, Keysar, & Kinzler, 2015; Liberman, Woodward, Keysar, & Kinzler,
2017)
Although superior cognitive control skills may put bilingual children in a
privileged position in terms of perspective-taking and referential choice, other factors
must also be considered as predictors of discourse-appropriate linguistic choices. The
bilingual language experience is, by its very nature, distributed across language, and –
at least in relative terms - bilingual children receive proportionally less input in each
language that monolingual children. Although relative amount of exposure is only an
indirect and imperfect approximation of input quantity (Carroll, 2017; De Houwer,
2014; Hurtado, Grüter, Marchman & Fernald, 2014), it has repeatedly been shown to
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correlate robustly with measures of language proficiency (Hoff, Welsh, Place &
Ribot, 2014; Unsworth, 2013).
It is plausible to expect a positive correlation between overall language skills
and the ability to select discourse-appropriate referring expressions. Hence, whatever
advantage superior cognitive control skills might confer to bilinguals when it comes
to referential choice – if any – it may be offset by lower language proficiency when
compared to monolingual children. Ryskin et al. (2014) make a similar claim to
account for the lack of a bilingual advantage in a spatial perspective-taking task with
adults. Some evidence that language proficiency may play a role comes from a
referential communication study (Fan, Liberman, Keysar, & Kinzler, 2015) which
also included measures of language proficiency (receptive vocabulary), cognitive
control, and fluid intelligence, in a group of monolingual 5-year-olds and two groups
of age-matched children who were either bilingual, or exposed to a multilingual
environment. The only significant effect was that of group with both the bilingual and
multilingual exposure children outperforming the monolinguals. Crucially the three
groups did not differ in terms of receptive vocabulary, and therefore it remains to be
seen whether bilinguals with lower language skills than monolinguals might be
adversely affected in a linguistic task.
Another variable that may potentially affect children’s linguistic and cognitive
performance is SES. SES is a complex construct and it is considered a proxy for
access to a range of economic, educational and occupational resources (Hauser &
Warren, 1997; McLoyd, 1998). Although there is a vast and expanding literature on
the relationship between SES and language and cognitive development, attributing a
causal role to SES in child development is not straightforward because SES is a
multifaceted notion and so are language and cognition (Duncan & Magnuson, 2012).
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For example, SES has been shown to affect vocabulary size but not utterance length
(Hoff-Ginsberg, 1998), grammar but not pragmatic development (Wells, 1986), and
the effects are greater for expressive than receptive vocabulary (Snow, 1999).
In monolinguals the complex relationship between linguistic and cognitive
development and SES is well documented (Hackman & Farah, 2009; Hackman,
Gallop, Evans & Farah, 2015). When it comes to bilingual children, there is inevitably
an added layer of complexity. In bilingual populations SES also has a predictive role
on language and cognitive skills, although it is not often easy to tease apart the
relative contribution of bilingualism and SES. In many studies there are significant
cultural differences between the bilingual and the monolingual groups, and the
immigrant status of the bilinguals may present an additional confound. A number of
studies have recently tried to disentangle SES from bilingualism (Calvo & Bialystok,
2014; Carlson & Meltzoff, 2008) and the main finding seems to be that both
bilingualism and SES independently account for the variance observed in linguistic
and cognitive tasks. The relationship between SES, bilingualism, and language and
cognitive performance is however complex (Gathercole, Kennedy & Thomas, 2015)
and is mediated by language exposure, age and the specific aspect of language (e.g.
vocabulary vs. grammar), or of non-verbal cognition being tested.
����������������
To date, the relationship between perspective-taking skills, cognitive control,
verbal WM, and referential choice has mostly been studied in the context of online
comprehension. Studies investigating the predictive role of executive function skills
in production have reported mixed results (Nilsen & Graham, 2009; Wardlow Lane,
2013; Ryskin et al., 2015; Torregrossa, 2017; Wardlow & Heyman, 2016).
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The first aim of the present study is to test whether cognitive control, as
measured by the Simon task, and verbal WM, as measured by backward digit recall,
are predictive of referential choice in a production task in which child participants
need to build a complex situation model and identify a target referent in settings in
which we manipulate the presence of discourse and visual competitors. The prediction
is that the Simon task score and the backward digit recall score will correlate
positively with the informativeness of the participants’ referential choices.
The second aim of the present study is to investigate the contribution of language
experience to perspective-taking abilities and referential choice. English-speaking
monolingual children and bilingual children with varying degrees of exposure to a
language other than English (henceforth the home language) are therefore included in
the study. Language experience is conceptualized here both in terms of cumulative
amount of exposure and use of the home language (Bilingual Profile Index, BPI, De
Cat, Gusnanto & Serratrice, 2017; De Cat & Serratrice, under review), and in terms of
language proficiency as measured by the Articles sub-test of the Diagnostic
Evaluation of Language Variation (Seymour, Roeper & de Villiers, 2003), a dialect-
neutral assessment for 4- to 9-year-olds, that minimizes the effects of language
exposure differences in bilingual and bicultural children. We expect that children with
better language proficiency – which is in turn likely to be predicted by the amount of
exposure and use of English – will be more sensitive to the presence of discourse and
visual competitors. It is also conceivable that language experience and language
proficiency would interact, such that bilingual children might display an advantage
only if their English proficiency falls within the range of their monolingual
counterparts – as shown by Fan et al. (2015).
Finally, studies of perspective-taking skills have typically investigated the
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comprehension and use of NPs containing disambiguating size or colour adjectives
(e.g. the small duck, the red square) that directly pick out an entity in a visual display
and are therefore not anaphoric (e.g. Nilsen & Graham, 2009; Wardlow & Heyman,
2016). In contrast, in the present study we are focusing on the use of anaphoric
expressions, i.e. third person pronouns vs. NPs, and on how the discourse and visual
contexts determine the choice of a referential expression for a target referent in the
presence of one or two antecedents that may be either visually present, linguistically
mentioned, both, or neither.
The experiment is modelled on the studies in Fukumura, van Gompel and
Pickering (2010) with monolingual adult participants where they manipulated the
linguistic mention and the visual presence of a competitor to a target referent.
Although Fukumura et al. (2010) did not address this issue, the use of an NP in
conditions in which a pronoun is ambiguous should – at least partly – be predicted by
cognitive control and verbal WM. Those participants that are more successful at
inhibiting their egocentric perspective, and have better WM resources to deal with a
complex scene, should be those that are sensitive to the presence of a discourse and
visual referent that is in competition with the target.
Our prediction is that, if - similarly to adults – children are sensitive to both
the linguistic and the non-linguistic features of the context in creating a discourse
model, they will produce more informative referential expressions, i.e. full NPs (e.g.
the princess, the cowboy) when the competitor is previously mentioned and when it is
visually present.
SES will be included as a predictor in the analyses alongside measures of
language proficiency, language exposure and use, cognitive control and verbal WM,
to assess the contribution that these child-internal factors might make to the use of
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anaphoric expressions in a demanding language production task.
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After receiving ethical approval for the study by the University Research Ethics
Committee of the second author’s institution, children were recruited in state primary
schools in the North of England. The final sample included 172 children attending
year 1 or year 2 of primary school (between the ages of 5 and 7), all of whom were
schooled exclusively in English. Half of the children (N = 87) were also exposed to a
language other than English at home; these children will be referred to as bilinguals.
In this study we adopted a broad definition of bilingualism that reflects the typical
situation of many classrooms in the UK where children are classified as learners of
English as an Additional Language (EAL) if ‘a first language, where it is other than
English, is recorded where a child was exposed to the language during early
development and continues to be exposed to this language in the home or in the
community.’ (DfE School Census Guide 2016-2017, p.63). Because of this
inclusionary criterion, the children in our bilingual group had a wide range of
exposure (as low as 9%) to 28 different home languages: Punjabi (21% of bilingual
participants), Urdu (17%), Arabic (9%), French (8%), Spanish (6%), Bengali,
Cantonese, Catalan, Dutch, Farsi, Greek, Hindi, Italian, Kurdish, Mandarin, Marathi,
Mirpuri, Nepalese, Pashto, Polish, Portuguese, Shona, Somali, Swedish, Tamil,
Telugu, Thai, Tigrinya (languages with no percentage indicator accounted for less
than 5% of the sample). Our bilingual group was therefore deliberately heterogeneous
to capture the variability of children who are currently considered as bilingual (EAL
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learners) in multilingual classrooms in the UK, and to capitalise on the notion of
bilingualism as a continuous measure.
������
In addition to the main referential communication task that is the object of this
study, we collected information on the children’s SES, on their exposure and use of
English and the home language, and tested their proficiency in English, their verbal
WM and their cognitive control skills.
Socio�economic Status (SES). The children came from schools in a range of
different catchment areas to ensure variation in SES. We collected information on
parental education and occupation via questionnaires. Children were allocated an SES
score on the basis of the highest level of occupation or education in the household
(either mother or father). Education was coded on a five-point scale (none, primary,
secondary, further, university), and the occupational data was coded according to the
reduced method of the UK National Statistics socio-economic classification. We used
the reversed occupational data scores to make the interpretation of the association
with the educational level data more transparent, so that a higher value represents an
advantage. As expected there was a strong association between the two measures (Χ2
(4, N = 174) = 83.57, p < 0.0001). We also found a weak but significant negative
correlation between level of bilingualism as measured by the children’s cumulative
amount of exposure and use measured by the Bilingual Profile Index - as described
below- and SES as measured by parental occupation (r = −.25, p = 0.0009).
Language exposure and use. We used a parental questionnaire to estimate the
bilingual children’s relative amount of exposure and use of English and of the home
language. The questionnaire, which includes both current and cumulative estimates of
the amount of exposure and use, is modelled on the BiLEC (Unsworth, 2013). The
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parents (usually the mother) completed the questionnaire in English, Bengali, Punjabi
or Urdu with the help of a bilingual assistant. They were asked to quantify the amount
of their child’s current exposure and use of the two languages on a typical school day,
at weekends, and during holiday periods. School days were divided into slots of one
hour before and after school during which children were exposed predominantly to
English. It is possible that children may have used the home language with some
same-language peers at school but because parents – and not teachers – were asked to
complete the questionnaire, we did not have access to this information and we
conservatively assumed that during school hours children only heard and used
English. Parents were asked about all of the child’s interlocutors, and to estimate on a
five-point scale how often they addressed the child in the home language (never,
rarely, half of the time, usually, always). We later converted the scores into discrete
percentage bands ranging from 0 (never) to 100% (always). Parents were also asked
to recall age of first exposure to English. To calculate the current relative amount of
exposure to English and the home language for a given child we extrapolated the
number of hours that the child spends with each interlocutor on a yearly basis, and we
multiplied this figure for the percentage of time the child used either English or the
home language with each interlocutor. The percentages for each of the child’s
interlocutors were added and then divided by the total number of hours of interaction
pooled for all interlocutors, if several interlocutors were present at the same time, the
estimate was divided by the number of interlocutors for the relevant time window.
The resulting was a percentage expressing the relative amount of input for English
and the home language. We applied the same method to the calculation of a relative
measure of child’s output, i.e. use of English or the home language. For the
cumulative amount of input/output in each language we firstly calculated the number
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of months of home language use only, i.e. before children were exposed to English –
this was 0 for the simultaneous bilingual children – we then multiplied the number of
months of bilingual exposure by the proportion of current input/output. The resulting
figure is the total number of months equivalent to full-time exposure to the home
language.
The use of parental questionnaires to collect information on quantity and
quality of child-directed input has obvious limitations and has lately come under
critical scrutiny (Carroll, 2017). Although we acknowledge the constraints of this data
collection method, we are also confident that it is a pragmatic solution whose validity
and robustness have been repeatedly confirmed (De Houwer, 2017; Paradis, 2017).
Current and cumulative measures of input and output in the home language
were highly correlated in our sample (current input and output: r = .90, p < 0.0001;
cumulative input and output: r = .95, p < 0.0001). Because we wanted to use both
dimensions of the language experience as predictors in our analysis but needed to
avoid collinearity for modelling purposes, we used Principal Component Analysis
(PCA) to decorrelate the two measures and create a composite score of cumulative
input and output which we call the Bilingual Profile Index (BPI, De Cat et al., 2017;
De Cat & Serratrice, under review). The PCA of cumulative input and cumulative
output yielded two principal components, the first of which captured 98% of the
variability (given the strength of the correlation between the two cumulative
measures). The BPI scores correspond to the loadings of that first component,
reversed (so that a higher score corresponds to more experience in the home
language) and aligned with a score of 0 for monolinguals. The BPI can be interpreted
as a cumulative and gradient measure of a bilingual child’s experience of their home
language, effectively close to the number of full-time months of exposure corrected
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for any imbalance between exposure and use. The range of the BPI in our sample is
from 0 to 96.
Language proficiency. We used the Articles sub-test of the Diagnostic
Evaluation of Language Variation - DELV (Seymour et al., 2003) as a measure of
language proficiency in English, the language of schooling. The DELV is a language
assessment of syntax, semantics, pragmatics and phonology for children between the
ages of 4 and 9. This test was specifically developed to neutralize dialectal differences
and it focuses on language structures that are common to all children from English-
speaking backgrounds regardless of the particular variety of English they speak. We
chose the Articles sub-test as an independent measure of language proficiency as it
taps into some of the same discourse-pragmatic skills that are required for the
appropriate use of referential expressions.1
Verbal working memory (WM). We used the Backward Digit Span task from
the Wechsler Intelligence Scales for Children (Wechsler, 1991) as a proxy measure
for children’s verbal WM capacity. The backward digit span was administered
according to the WISC-IIIUK instructions: for each digit span the experimenter
administered two trials, regardless of whether the first trial was passed or failed, and
discontinued the test after failure on both trials of any item. Backward digit recall is
one of three complex memory span measures (the other two being listening recall and
counting recall) that in a confirmatory analysis were shown to load onto one single
1 Performance in this proficiency task is significantly correlated with performance on
other language proficiency measures collected as part of our larger study including
the School-Age Sentence Imitation Task (Marinis, Chiat, Armon-Lotem, Gibbons &
Gipps, 2010). See De Cat & Serratrice (under review, https://osf.io/wkgv7/) for
details.
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factor by Gathercole, Pickering, Ambridge and Wearing (2004). Unlike forward digit
recall, which only requires the storage and immediate recall of a sequence of spoken
items and taps into the phonological loop, backward digit recall implies both the
phonological loop, for the storage of items, and the central executive, for the
additional processing in the reversing of the digits.
Cognitive control. Children were administered a computer-based version of
the Simon task (Simon & Wolf, 1963) programmed and run via E-Prime. The Simon
task is considered a complex response inhibition task (Garon, Bryson & Smith, 2008).
because it involves moderate WM demands in addition to the inhibition of a prepotent
response. Participants need to hold a rule in mind (press the left button when you see
x, press the right button when you see y), respond according to this rule (physically
press the key), inhibit a prepotent response when the rule changes and respond
accordingly (press left button when you see y, press the right button when you see x).
The Simon task is one of many complex inhibition tasks that have been used
in the developmental literature to measure children’s ability to inhibit a prepotent
response while responding to a salient conflicting response option (see Garon et al.,
2008 for a comprehensive review). With specific reference to the bilingual-
monolingual comparison, previous studies have shown that bilingual children
outperform monolingual peers only in tasks that assess the interference suppression
component of cognitive control (Bialystok & Shapero, 2005; Qu, Low, Zhang, Li &
Zelazo, 2016), but not in tasks that assess response inhibition alone (Martin-Rhee &
Bialystok, 2008).
Children sat in front of a 15.6” computer screen and used an E-Prime serial
response button box with colour-coded buttons (red on the left and green on the right).
Children started with 8 practice trials followed by 48 test trials; there was no neutral
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condition in which the coloured square would appear in the middle of the screen.
Accuracy and Reaction Times (RTs) were automatically recorded by E-Prime. The
index of cognitive control abilities used as a predictor in the present study
corresponds to the modelled score in the Simon task, i.e. children’s score adjusted for
age, SES, bilingual experience (indexed by the BPI), and accuracy at the previous
trial.2 These correspond to the significant predictors of a Cox Proportional Hazard
regression analysis, as reported in detail in De Cat et al. (2017). The Cox PH model
captures response accuracy and speed within the same analysis, so the resulting score
combines both aspects of children’s performance.
Table 1 provide descriptive statistics for the monolingual and bilingual groups:
Insert Table 1 here
���������������"���������
Following the design of the studies in Fukumura et al. (2010), the experiment
manipulated the visual presence and the linguistic mention of a competitor to a target
referent in a 2x2 design in four conditions: competitor present and mentioned,
competitor present and not mentioned, competitor absent and mentioned, competitor
absent and not mentioned. There were five items in each of the four conditions and
ten filler items. Each experimental item consisted of a set of two coloured
photographs of iconic Playmobil characters (e.g. fireman, cowboy, ghost, queen),
while the fillers included coloured geometric shapes and animals. Both the first and
the second photograph in the experimental set always included the target referent (e.g.
a fireman). In the competitor present conditions another referent of the same gender
2 The modelled score was obtained using the predict function of the survival package
in R (version 2.38.3), which was used for the analysis.
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also appeared in both photographs (e.g. a fireman and a pirate). Half of experimental
items contained characters of feminine gender, and the position of the target and the
competitor was counterbalanced throughout the experiment.
See Figures 1 and 2 for examples of experimental items in the competitor
visually present or absent conditions, and the Appendix for a full set of experimental
and filler items.
Insert Figure 1 and Figure 2 here
The first photograph in each set was presented alongside a digitally recorded
sentence spoken by a female native speaker of Northern British English. The sentence
was a passive whose subject contained a genitive phrase where the possessor was the
animate target referent and the possessum was an inanimate entity (e.g. The fireman’s
bed has been made). In the conditions in which the competitor was mentioned it
appeared in the passive’s by-phrase (e.g. The fireman’s bed has been made by a
pirate).
The rationale for embedding the target referent as the possessor in a genitive
phrase (e.g. The fireman in The fireman’s bed) was to reduce its accessibility and thus
generally decrease the likelihood that participants would only ever use pronouns in
their continuation. It also allowed us to tease apart sentence-initial position from
topichood. Like Fukumura et al. (2010) we also wanted to ensure that the bias
towards using a pronoun for a highly salient subject antecedent would not completely
obliterate the role of the visual context. The photographs were embedded in a
PowerPoint presentation. The second picture appeared after the first had disappeared
off the screen and was accompanied by the pre-recorded prompt “And now…“.
!�����
The children were tested on school premises. Two female experimenters took
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part in the task; experimenter A sat next to the participant; the participant sat in front
of a laptop computer and the two were separated by a divider so they could not see
what the other was looking at but they could see each other. Experimenter B
introduced the task to the participant as a communication game and explained that the
aim was to give instructions to experimenter A so that she could re-create the scenes
in the child’s pictures with the toys that she was given by experimenter B.
Experimenter B pressed the space bar on the child’s laptop on each trial to start the
experiment and to move on to the next item. Before the experiment started there were
two practice trials with feedback. No children had to be discarded for not
understanding the task. At the start of each trial experimenter B pressed the space bar
and the first picture appeared on the computer screen accompanied by the pre-
recorded linguistic description (e.g.. “The fireman’s bucket has been filled (by a
musician)”) lasting an average of 4000 ms. The space bar was pressed again at the
end of the sentence and the target picture would appear accompanied by the prompt
“And now…”. This was the participant’s cue to start giving directions to experimenter
A to arrange the toys to recreate the scene that the child would describe (e.g. And now
the fireman/he/the man is carrying the bucket). Experimenter A had the same toys
that were present in the child’s picture. When the participant had completed their
instruction they looked round the divider to see whether the experimenter’s toy
arrangement matched the photograph on their computer screen. The experimenter
remained in their seat, they showed the participant their toys and asked “Like that?”.
Whenever the participant used an under-informative pronoun, experimenter A always
chose the competitor to give the participant indirect feedback about their level of
underinformativity.
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Participants’ instructions to experimenter A were digitally recorded and
transcribed using CHAT for CHILDES (MacWhinney, 2000); utterances were later
imported into Excel and coded for the following features: mention of target referent
(1= target referent; 0 = competitor); label used (repeated name from the preamble
sentence, e.g. the king; an alternative label in the same semantic field– e.g. the prince
instead of the king; an alternative label that only matched the referent in gender, e.g.
the man instead of the king, the lady instead of the dentist); discourse integration (1=
pronouns and definite NPs anaphorically referring to the target referent- e.g.
he/she/the queen; 0 = indefinite pronouns – e.g. somebody – and indefinite NPs – e.g.
a man - that do not make clear anaphoric reference to the target).
The “discourse integration” coding operates a binary distinction between
anaphoric and non-anaphoric expressions; the “label used” coding provides a more
fine-grained distinction within different types of anaphoric referential expressions.
While the king, the prince, the man are all definite NPs, they vary along a continuum
of disambiguating information. We deliberately chose stereotypical and easily
identifiable referents for the experimental items (i.e. king, fireman, astronaut, queen,
nurse, etc.). To be maximally informative in the task, participants should ideally have
used the label that was provided in the preamble description associated with the first
photograph in the experimental pair. Using a different and less informative label
might lead to potential ambiguity that would, in turn, increase as a function of the
label’s lack of informativeness. So, in the case of a label in the same semantic field
(e.g. prince instead of king) the likelihood of ambiguity would not be as high as in the
case of a highly underspecified definite NP like the man that would give experimenter
A only a vague cue to select the appropriate target toy to reconstruct the scene, and
would be just as underinformative as a third person or an indefinite pronoun.
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�
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Table 2 provides descriptive statistics for the results of the DELV Articles
sub-test (language proficiency), the backward digit recall task (verbal WM) and the
Simon task (cognitive control) for the monolingual and the bilingual groups. Note that
the scales are different for the three measures. For the DELV, it is accuracy
proportion from 0 to 1; for the backward digit recall it is the number of accurately
recalled digits from 0 to 4 (as a score), and for the Simon task it is an index of
cognitive control adjusted for age, SES, bilingual experience and accuracy at the
previous trial; negative scores indicate better cognitive control skills.
Insert Table 2 here
A linear regression model fitted using the lme4 package (version 1.1.11) in R
(version 3.2.4) to the overall score in the DELV Articles sub-test showed that
performance was negatively correlated with the BPI (t(168) = -2.90; p = 0.004); as
expected, bilingual children performed more poorly than monolinguals overall,
greater exposure and use of the home language was correlated with lower proficiency
scores. There was no significant effect of the BPI in the verbal WM task (t(181) = -
0.29; p = 0.77). For the Simon task the results of a Cox-P Regression model showed
a near-significant effect of group (X2(1) = 3.8, p = 0.05) and a significant effect of
home language experience over and above the effect of group, as the BPI was a
positive predictor (X2(1) = 12.13, p = 0.0005). There was however no significant
interaction between bilingualism and cue congruency, and hence no Simon effect in
the strict sense (in line with previous studies).
We conducted three analyses to address the role of cognitive control, verbal
WM, cumulative home language exposure and use, SES, and language proficiency on
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the children’s use of referential expressions. In the first analysis, following Fukumura
et al. (2010), our DV only included exact repetitions of the target referent named in
the context sentence vs. the use of third person pronouns. Two further analyses were
necessary to capture the broader picture. In the second analysis, we included all
referential expressions that made anaphoric reference to the target and investigated
their informativeness by creating a binary DV: (1) underinformative expressions:
third person singular pronouns (e.g. he/she) and underinformative definite NPs – e.g.
the man instead of the king, the lady instead of the queen; and (2) definite NPs that
were either exact repetition of the definite NP in the preamble sentence, or
semantically related labels (e.g. the prince instead of the king, the singer instead of
the musician).
The third analysis identifies the factors that predict lack of discourse
integration. We used a two-way distinction between indefinites signalling a lack of
anaphoric discourse integration (i.e. indefinite NPs and indefinite pronouns), and
pronouns and definite NPs that made anaphoric reference to the target.
We fitted generalized linear mixed models using the lme4 package (version
1.1.15) in R (version 3.4.4). The models were fitted incrementally by adding
predictors one by one and retaining them only if they improved the model fit, yielding
a significant reduction in AIC and a significant R-squared value, with model
comparison estimated by likelihood ratio tests (Baayen, 2008). In each of the three
analyses we treated item as a random factor, participant was not included as random
factor because it would compete with the fixed factors capturing participant-related
variables such as the BPI, SES or proficiency. We tested for the significance of the
following fixed factors: the presence/absence of a discourse or a visual competitor,
the Simon task score (cognitive control), the backward digit recall score adjusted for
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age and proficiency (verbal WM), the DELV Articles sub-test score (language
proficiency), the BPI score (cumulative home language use and exposure), the SES
score, and age (in months). Age and Simon task scores were centered to facilitate the
interpretation of the models. The following interactions were also tested in all
analyses: visual competitor x discourse competitor (yielding the 4 experimental
conditions), discourse competitor x each participant-related predictor (BPI, SES, WM,
cognitive control), visual competitor x each participant-related predictor (BPI, SES,
WM, cognitive control), BPI x SES, BPI x proficiency, WM x proficiency. Gender
was added as a covariate. Age correlated strongly with other participant-related
predictors and could therefore not be included in the models without resulting in lack
of convergence. In the following we report the optimal models.
To be consistent with the protocol in Fukumura et al. (2010) we excluded
references to the competitor. The total amount of data points expected, given the
number of participants (172) and items (20) was 3440, there were 66 no response
therefore the actual number was 3374. We excluded the following data from all
analyses: 86 items were excluded because of reference to the competitor, or
because the utterance was (partly) unintelligible. We also excluded a problematic
experimental item (N = 115) for a total of 201 items, i.e. 6% of the data.
In the first analysis, the repeated name was expected to feature as the subject
in the first sentence that participants produced to describe the second picture in the
experimental item. As in Fukumura et al. (2010) we excluded a further 155 tokens
where the target referent was indefinite or lacked a determiner, as well as 310 tokens
that were not exact repetitions of the named referent. Altogether, 19% of the data was
excluded from the first analysis. The remaining responses included a total of 1766
NPs and 942 pronouns.
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The dependent variable was the likelihood of producing a definite NP (as
opposed to a pronoun) to identify the target referent in the second picture of the
experimental items. We used logistic regression to model the probability (in terms of
logits) associated with the values of the dependent variable. NP use was predicted
by the visual presence of a competitor (z = 3.21, p
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the Simon task score and the presence of a discourse competitor (z = 2.12, p = .03).
Further, there was an interaction between language experience
(monolingual/bilingual) and language proficiency (below/above the monolingual
mean) (z = -2.15, p = .03) whereby monolingual children below the language
proficiency mean used more NPs than bilingual children below the language
proficiency mean. For children above the language proficiency mean there was no
difference as a function of language experience as shown in Figure 5.
Insert Figure 5 here
As children used NPs other than the repeated name in their story continuation,
in a second set of logistic regression analyses, we investigated the level of
informativity of the label used to identify the target referent. The dependent variable
included all the referential expressions that children used to identify a target referent
where there was evidence of an attempt at discourse integration; we therefore
excluded all bare nouns, indefinite NPs and indefinite pronouns (155 items), with
8.3% of data excluded in total. The dependent variable was binary and had two
levels: (1) underinformative expressions - third person singular pronouns and less
informative definite NPs (e.g. the man; the lady), and (2) more informative definite
NPs (repeated NPs from the preamble, semantic substitutions, e.g. the prince for the
king). Using the WM score where language proficiency and age were partialled out
did not allow the model to converge, we therefore used the raw WM score. The
optimal model shows that children were more informative in the presence of a visual
competitor (z = 2.15, p = .03), while the mention of a discourse competitor had no
significant effect (z = -1.15, p = .25). The interaction between WM and language
proficiency was a significant predictor of informativity (z = 9.59, p < .001), while
none of the other predictors made a significant contribution to the model.
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As we did earlier, we repeated this analysis including the mean monolingual
language proficiency as a threshold to investigate a potential language proficiency
disadvantage for bilingual children in the production of informative NPs. The effect
of visual competitor was significant (z = 2.14, p = 0.03), as was the effect of WM (z =
4.88, p < .001). Similarly to what we found in the first set of analyses, monolingual
children (z = 3.56, p < 0.001) and children with language proficiency above the
monolingual mean (z = 9.51, p < 0.001) produced significantly more informative NPs.
The significant interaction between language proficiency and language experience (z
= -2.18, p = 0.03) showed once again that there was no difference as a function of
language experience for children whose proficiency was above the monolingual
mean, but for those below the mean threshold monolinguals produced more
informative NPs.
Our third and final set of analyses investigated the possible causes for not
encoding the target referent with a definite NP or a pronoun (which resulted in
exclusion from the first and the second analyses). This third analysis revealed
whether children were able to integrate the discourse information provided in the
preamble – where the target was introduced with or without a competitor – and the
target in their own scene description. The dependent variable was the definiteness of
the target expression used, a proxy measure for discourse integration. Only bare
nouns were excluded (44 items), on top of the items excluded from all analyses. The
excluded items amounted to 7.3% of the data in total. In this logistic regression
analysis, the coefficients indicate the likelihood of using a definite expression, thereby
integrating the target expression with the preceding discourse without discriminating
further between more informative full NPs and less informative pronouns. Very few
items displayed lack of discourse integration: 3% in monolinguals and 4% in
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bilinguals.
The presence of a visual competitor adversely affected discourse integration (z
= -2.87, p
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discourse and visual information in a complex referential communication task.
Cognitive control skills, verbal WM, , language proficiency, language exposure and
use, and SES were investigated as predictors of the choice of discourse-appropriate
anaphoric expressions in the task.
��������������������������������������
With the exception of analysis 2, cognitive control – as indexed by the Simon
task score – was a significant predictor of NP use. In analysis 1 and 3 – when a
language proficiency threshold is introduced as a predictor - better cognitive control
predicted sensitivity to the presence of a discourse competitor. In analysis 3, better
cognitive control also predicted discourse integration in the absence of the additional
language proficiency threshold.
Within the context of the current experiment, the manipulation of the presence
and discourse mention of a competitor to the target referent unpredictably varied the
need to resolve a referential conflict. In the condition in which the target had no
linguistic or perceptual competition no conflict arose. However, in the remaining
three conditions the discourse and/or perceptual presence of a competitor created a
referential conflict. The resolution of this conflict required the children to both inhibit
the preferred choice of a pronoun for a recently mentioned target referent, and to use a
more informative referential expression (a NP) instead for the benefit of their
addressee. The unpredictability of an upcoming potential referential conflict
necessitated a level of monitoring that we hypothesised would correlate with their
cognitive control abilities as indexed by the performance on the Simon task.
We never found an interaction between language experience and cognitive
control in the prediction of NP use suggesting that cognitive control abilities
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conferred an advantage to both groups of children independently of bilingualism,
contrary to our initial hypothesis. This could be because the bilingual advantage for
cognitive control abilities in this group of children was modest (albeit significant, see
also De Cat et al., 2017). In our predictions we also hypothesised that whatever
bilingual advantage there might be in cognitive control might be offset by bilingual
children’s lower proficiency skills. We did find, at least in analysis 1 and 3, that the
degree of exposure and use of the home language negatively correlated with NP use
before controlling for language proficiency. In an additional set of analyses we
investigated whether keeping language proficiency constant for the monolingual and
the bilingual children might mitigate the proficiency disadvantage against the
bilinguals. Using the mean performance of the monolingual children on the language
proficiency task we split the groups above and below the monolingual mean, and we
did repeatedly found that those bilingual children that had language proficiency skills
above the monolingual mean were no different from their monolingual counterparts in
the use of informative NPs. They were however no better, as might be expected on the
assumption of a bilingual advantage in cognitive control. The reason for this lack of
bilingual advantage, once proficiency was controlled for, is likely to stem from the
heterogeneity of our bilingual group. We deliberately had very broad selection criteria
for the bilingual children in our recruitment schools so that we could include all of the
children that were classified in the UK education system as having English as an
additional language (EAL learners). This resulted in children who differed vastly in
the cumulative amount of input and output and in the range of languages spoken. As
our understanding of the bilingual cognitive advantage is progressively refined we
now know that a large number of variables, both at the level of the individual
bilingual speakers and at the level of the tasks used (Mishra et al., 2012), can
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